Herpes simplex virus (HSV) is the most common infectious cause of blindness in the United States. Thirty to 60% of ocular HSV patients have a recurrence within 1 to 2 years. One of the fundamental problems in herpes virus research is to define the state and activity of the viral genome during periods of latency. The presence of this genome is the source of recurrent disease during latent infection. Development of antiviral therapy directed at eradication of latent virus has been unsuccessful. How viral latency is established, how the viral genome is maintained in neurons and the mechanism by which the virus reverts to an active disease state are unknown. Understanding the HSV latency phenomenon (probably a basic biological mechanism) may help to understand the course of herpetic disease in other parts of the body. The goal of this project is to investigate latent and reactivating ganglionic infection by means of an improved, in situ nucleic acid hybridization technique. A radiolabeled cloned plasmid HSV DNA probe with a high degree of selectivity for viral DNA and RNA and a high specific radioactivity (2 million CPM/Mug HSV DNA) will be used to identify and characterize foci of active and latent viral infection in the trigeminal ganglia, CNS projection areas of the trigeminal nerve, and superior cervical ganglia of rabbits and mice. Modification of the stringency of the hybridization conditions will help to detect any activity of the HSV genome during latency (ie, viral RNA production). Viral reactivation by direct ganglionic electrical stimulation or iontophoresis of epinephrine will be used to precipitate episodes of virus reactivation in trigeminal ganglia. In situ hybridization will then be used to evaluate changes in latently infected neurons following reactivation. Systemic antiviral therapy will be used in animal models of HSV infection; colonization of ganglia during acute ocular HSV infection and modulation of latent infection will be monitored for effect of antiviral therapy on foci of latent infection and consequent effects on recurrent viral disease. Analogous experiments will be carried out in an in vitro drug-suppression model. Non-toxic, highly selective, potent antiviral drugs such as acyclovir, bromovinyldeoxyuridine, BW759 and a recently developed pro-acyclovir compound will be evaluated for suppression of HSV infection in both in vivo and in vitro models.